Here's what we know so far: ZeniMax Media, parent to Bethesda Softworks, filed a Elder Scrolls V: Skyrim under the name "Hearthfire." They've also trademarked the infamous "Fus Ro Dah," as well as the title "Dragonborn." Any Skyrim player worth their salt knows these two terms, and since they're already heavily involved with the game, it's unlikely that these last two will be the title of any future DLC. That leaves us with "Hearthfire."
Like "Fus Ro Dah," "Hearthfire" has some connection with Skyrim lore. As many players already know, "Hearthfire" is one of the months in the Elder Scrolls universe, and is essentially the equivalant of our own September, so it may qualify as the time when ZeniMax, or by proxy, Bethesda, might make some kind of an announcement concerning another DLC. But this is unlikely, as trademarking goes a bit beyond necessity for just making an announcement. Bethesda has acknowledged that they've planned at least two DLC packs planned for Skyrim, and with Dawnguard already out, "Hearthfire" is the main contender, as the trademark application specifically applies to "Computer game software for use with computers and video game consoles; downloadable computer game software offered via the internet and wireless devices."
But there may be some possible clues we can find by examining the month. According to the Elder Scrolls wiki, there are some annual events that are celebrated during that time, seen below. Most of the events are celebrated outside the area of Skyrim.
* On the 1st - Rites of Moawita, practiced by the Psijic Order.
* On the 6th - Khurat, a time when scholars are taken into varying priesthoods, celebrated
* On the 12th - Riglametha, an offering for the graces of gods, is held
* On the 19th - Children's Day celebrated.
For the majority of these celebrations, holidays, etc., details have not been elaborated on, and seem to be non-events for the most part. However, there is one event that seems like it has some potential. Taking place on the 3rd is "Tales and Tallows," a celebration of necromancy feared by many citizens. It's not mentioned as region specific, and seems to be some notoriety surrounding the event. Citizens tend to avoid the streets during this time.
The storyline of Skyrim doesn't center around necromancy itself, but it is an option for gameplay depending on how you build your character. Also, the College of Winterhold allows the practice to some degree. Because of the notoriety surrounding it, it isn't addressed within detail, so there is a lot of potential room for expansion.
Of course this is all speculation, so don't take any of it as fact. Bethesda has yet to give any clues or details for "Hearthfire," or any possible DLC. The latest DLC, Dawnguard, is out now for Xbox 360, and is expected out on PS3 soon.
